1. Field of the Invention:
This invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having as a magnetic recording layer a ferromagentic film excelling in travelling stability and durability.
2. Description of Prior Art:
Today, magnetic recording media are extensively used in audios, videos, computers and magnetic disks. In consequence of the growth of their utility, volumes of information to be stored in the magnetic recording media are incessantly expanding year after year. The desirability of these magnetic recording media possessing improved recording density, therefore, is commanding growing recognition.
The non-binder type magnetic recording medium, i.e. the magnetic recording medium formed of a ferromagnetic film, which enjoys easier reduction of wall thickness and higher saturation magnetization than the coating type magnetic recording medium problems with respect to corrosion, impact, and frictional strength. It has the possibility of sustaining wear or even breakage owing to the high-speed motion it is required to produce relative to the magnetic head during the recording, replaying, and erasing of magnetic signals. To be more specific, since the magnetic recording medium provided with a ferromagnetic film produced by such a method as electroplating, non-electrolytic plating, spattering, vacuum evaporation or ion plating contains no binder therein, it has the possibility of yielding the magnetic recording layer thereof to excoriation or destruction due to the friction which the magnetic recording medium generates during its sliding contact with the magnetic head.
The magnetic recording medium which consists of a ferromagnetic.film has a surface susceptible of corrosion. As the corrosion advances, it deteriorates the practical properties of the magnetic recording medium such as head touch and wear resistance and manifests and adverse effect on the electromagnetic conversion property thereof as well.
A method which provides for applying a lubricant on the surface of the magnetic metal film (Japanese patent publication No. SHO 39(1964)-25246) has been proposed as a solution. This method, however, fails to provide durable surface lubrication as expected because the lubricant on the surface is wiped away by the magnetic head, for example. Naturally this method cannot be expected to impart rustproofness, durability, etc. to the treated film.
As means of continuously furnishing the surface of the magnetic recording layer with lubrication, there has been proposed a method which provides for in forming on the opposite side of the magnetic recording layer a lubricating layer (backcoat layer) composed principally of a liquid or semisolid lubricant and an organic binder (Japanese patent publication No. SHO 57(1982)-29769). This method supposedly manifes excellent effect with respect to changes of durability (degree of scratching and excoriation) and dynamic friction coefficient because the lubricant exuding to the rear surface of the magnetic recording layer passes into the magnetic recording layer when it is wound in a roll and ensures constant supply of the lubricant to the surface of the magnetic recording layer. When the ferromagnetic film is not provided with a topcoat layer and only the backcoat layer is allowed to contain the lubricant as contemplated by this method, the level of friction between the magnetic film and the magnetic head is still high enough to impair the smoothness of travel of the magnetic film and the resistance of the magnetic film to corrosion and rusting is not adequate.
An object of this invention, therefore, is to provide a novel magnetic recording medium.
Another object of this invention is to provide a ferromagnetic film type mangetic recording medium improved in resistance to wear, durability and travelling property.